1. Field of the Invention
This invention relates to a pixel compensating circuit, a method for compensating pixels, and an image taking apparatus employing such pixel compensating circuit, wherein defect pixels included in a video signal obtained from an image sensor are compensated.
2. Description of the Related Art
In a digital still camera and a video camera, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) image sensor is widely used in a solid state image taking apparatus.
In such image sensor, defect pixels which do not function well are included sometimes among pixels of the image sensor. For example, when such image sensor product is carried by an airplane, there is a problem, wherein some of pixels of the image sensor are sometimes damaged by the passage of a cosmic ray having high energy. Those image sensors having such defect pixels are wasted at assemble stage.
However, this causes high cost in total, so that various methods for compensating defect pixels have been considered so far. For example, there are a sampling hold method where a value of a pixel immediately before (immediate left) a defect pixel is employed as the value for the defect pixel, an averaging method where an average value of two pixels located immediately before and immediately after the defect pixel is employed, and the like. Further, there is another method called an edge detecting method where edge information is detected by taking differences between color information of the defect pixel and color information of adjacent pixels located immediately after the defect pixel, and the compensation is carried out from defect pixel which is thought to be small in its effect.
However, in the above mentioned sampling hold method and the averaging method, there is a problem wherein possibility of carrying out a significant erroneous compensation are high when abrupt edges overlap on the defect pixel, and adequate compensation result can not be expected. Particularly, even when two or more than two pixels in a row have defects, the compensation by the above mentioned methods is carried out uniformly, so that there is a risk of standing out the defect pixel by contrast. From this point of view, although the edge detecting method is one of excellent compensating methods, but the edge detecting method has a problem in which when the compensation is erroneously carried out, the defect pixel may have a color different from periphery because the edge detecting method carries out the compensation by focusing on only one color information.